The present invention relates generally to polishing systems for polishing a surface of a substrate to a desired surface profile or finish and, more particularly, to an automated polishing system and method of polishing a surface of a substrate during a polishing cycle using computer control.
Automated polishing systems have been developed to polish surfaces of optical and non-optical components to precise surface finishes and surface profiles through an abrasion process using a polishing tool and a polishing slurry. For example, automated polishing systems have been used to obtain precise surface finishes and profiles on spherical and aspherical optical lenses using a computer-controlled polishing spindle that moves a rotating polishing tool across the surface of a rotating lens according to a pre-programmed tool path. The tool path may be defined by coordinates along three orthogonal axes so that the polishing tool follows the general profile of the lens during a polishing cycle to obtain the desired surface finish and profile on the lens. The velocity of the polishing tool is varied as it traverses the lens so that more lens material is removed in areas of relatively slow traverse.
Prior to the polishing cycle, the profile of the lens to be polished is measured and compared with a reference lens profile stored in a computer. The computer determines whether the actual surface profile of the lens differs from the reference lens profile by a predetermined error amount. If so, the computer executes a material removal algorithm that determines a predetermined tool path for the polishing tool to follow across the surface of the lens and the required velocity profile of the polishing tool so that the desired surface finish and profile will be obtained during the polishing cycle.
The amount of material removed from the surface of the lens is determined by the polishing pressure applied by the polishing tool to the surface of the lens and also by the velocity profile of the polishing tool as it traverses the lens during a polishing cycle. The amount of material removed from the surface of the lens is increased with either an increase in the pressure applied by the polishing tool to the surface of the lens or an increase in the dwell time of the polishing head in a particular annular region of the lens.
Accordingly, in the event fluctuations occur in the pressure applied by the polishing tool to the surface of the lens as it traverses the lens, without a change in the velocity profile of the polishing tool to compensate for the fluctuation in polishing pressure, the lens will not obtain the desired surface finish and profile during the polishing cycle. In those areas of increased polishing pressure, more lens material will be removed than desired, while other areas receiving a lighter polishing pressure will not have enough material removed to obtain the desired surface finish and profile. These pressure fluctuations may occur due to positioning inaccuracies in the polishing system mechanics responsible for moving the polishing spindle during the polishing cycle, and also to the surface profile geometry encountered by the polishing tool during the polishing cycle.
Thus, there is a need for an automated polishing system for optical and non-optical components that is not susceptible to polishing pressure fluctuations during a polishing cycle so as to provide uniform surface finishes and accurate curve profiles on the polished component.
The present invention overcomes the foregoing and other shortcomings and drawbacks of automated polishing systems and polishing methods heretofore known. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
The polishing system of the present invention is particularly adapted to polish a surface of a substrate, such as a surface of an optical mold pin, to a desired surface profile and finish under the automated control of a computer during a polishing cycle. The polishing system includes a polishing spindle assembly that is adapted to support the rotating polishing tool and is operable to move in at least one of a direction toward and away from the rotating mold pin to contact the polishing tool on the surface of the mold pin with a predetermined torque on the polishing tool during the polishing cycle. The polishing tool is contacted under pressure with the surface of the mold pin during a polishing cycle to obtain the desired surface profile and finish on the mold pin. The polishing tool includes a polishing head that is covered with an abrasive polishing paste and placed into contact with the mold pin during the polishing cycle to remove material from the surface of the mold pin through abrasion.
A positioning mechanism is operatively connected to the polishing spindle assembly and is operable to move the polishing spindle assembly in at least one of a direction toward and away from the mold pin. In one embodiment, the positioning mechanism has three (3) orthogonal axes of translation to guide movement and control positioning of the polishing spindle assembly and the polishing tool relative to the mold pin during a polishing cycle.
A control is operatively coupled to the positioning mechanism and the polishing spindle assembly. The control is operable to adjust positioning of the polishing spindle assembly in at least one of a direction toward and away from the substrate to maintain the torque on the polishing tool substantially constant, and therefore the contact pressure applied by the polishing tool to the surface of the mold pin substantially constant, during the polishing cycle.
In accordance with one aspect of the present invention, a torque sensor is associated with the polishing spindle assembly and is operatively coupled to the control. The torque sensor is operable to sense a torque on the polishing tool during the polishing cycle. The control is responsive to the torque sensed by the torque sensor to adjust positioning of the polishing spindle assembly in at least one of a direction toward and away from the mold pin to maintain the torque on the polishing tool substantially constant during the polishing cycle. The torque sensor may be mounted to remain substantially stationary during the polishing cycle or, alternatively, the torque sensor may be mounted to rotate during the polishing cycle.
By maintaining the torque substantially constant on the polishing tool during the polishing cycle, the polishing system of the present invention is able to provide uniform surface finishes and accurate curve profile on the surface of the mold pin. The polishing system maintains a constant polishing pressure on the polishing tool during the polishing cycle to accurately and reliably remove material from the surface of the mold pin so that the desired surface finish and curve profile is obtained.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.